MIMO systems with active scatters and their performance evaluation

Abstract

Presented are MIMO communications architectures among terminals with enhanced capability of frequency reuse by strategically placing active scattering platforms at right places. These architectures will not depend on multipaths passively from geometry of propagation channels and relative positions of transmitters and those of receivers. For advanced communications which demand high utility efficiency of frequency spectrum, multipath effects are purposely deployed through inexpensive active scattering objects between transmitters and receivers enable a same frequency slot be utilized many folds such as 10×, 100× or even more. These active scatters are to generate favorable geometries of multiple paths for frequency reuse through MIMO techniques. These scatters may be man-made active repeaters, which can be implemented as small as 5 to 10 watt lightbulbs for indoor mobile communications such as in large indoor shopping malls. The architecting concept can be certainly implemented via mini-UAV platforms parking on tops of light-poles, or tree tops, or tops of stadiums, or circulating in small “figure-8” or small circles slowly. This systems can be pushed to facilitate >>100× frequency reuses among users. It may be one of possible solutions for 5G deployment and many other applications which needs high efficiency in frequency utility.

What is claimed is: 
     
       1. A communications system comprising:
 at least one receiver having a plurality of receiving elements; 
 a transmitter comprising:
 a plurality of transmitting elements configured to transmit one or more signals to the receiving elements of the at least one receiver via multiple wireless propagation channels; 
 a beam-forming network having input ports and output ports, receiving input signal streams at the input ports and outputting the one or more signals as shaped beams based on a set of composited transfer functions to the transmitting elements; and 
 a channel measurement unit configured to perform measurements of components of channel status information and generate the set of composited transfer functions by computing linear combinations of the measured components of channel status information; and 
 
 at least one active scattering platform located within the wireless propagation channels between the transmitter and the at least one receiver, the at least one active scattering platform being configured to receive and amplify the transmitted one or more signals and re-radiate the amplified received one or more signals toward the at least one receiver, 
 wherein the measured components of channel status information include a set of point-to-point transfer functions characterizing at least a propagation path between one of the transmitting elements and one of the receiving elements, wherein the composited transfer functions are point-to-multipoint transfer functions characterizing propagation paths between the input ports of the beam-forming network and one or more of the receiving elements, and wherein each of the composited transfer functions is a linear combination of the point-to-point transfer functions. 
 
     
     
       2. The communications system of  claim 1 , wherein the channel measurement unit comprises a single-input to multiple-output processor for generating the composited transfer functions. 
     
     
       3. The communications system of  claim 1 , wherein the at least one active scattering platform is stationary or relocatable. 
     
     
       4. The communications system of  claim 1 , wherein the at least one active scattering platform is mobile. 
     
     
       5. The communications system of  claim 1 , wherein the channel measurement unit groups all paths from one of the transmitting elements to one of the receiving elements and generates a corresponding point-to-point transfer function. 
     
     
       6. The communications system of  claim 1 , wherein the at least one active scattering platform is implemented as a lightbulb. 
     
     
       7. The communications system of  claim 1 , wherein the at least one active scattering platform has shapeable receiving antenna gain or shapeable transmitting antenna gain or both. 
     
     
       8. The communications system of  claim 1 , wherein the at least one active scattering platform has at least one of the group of variable amplification gain, shapeable receiving antenna gain, and shapeable transmitting antenna gain. 
     
     
       9. The communications system of  claim 1 , wherein the channel measurement unit comprises an optimization unit to perform optimization by continuously updating complex weighting for the one or more signals to be transmitted by the transmitting elements. 
     
     
       10. The communications system of  claim 9 , wherein the optimization unit performs optimization using beam shaping techniques under performance constraints associated with locations indexed by identification of the at least one receiver or by identification of each of the receiving elements. 
     
     
       11. The communications system of  claim 10 , wherein the optimization unit uses optimization algorithms to obtain a set of optimized weights for a next update of complex weighting based on differences between current performances and the performance constraints. 
     
     
       12. The communications system of  claim 10 , wherein the performance constraints comprise performance constraints on a set of orthogonal beams. 
     
     
       13. The communications system of  claim 10 , wherein the performance constraints comprise performance constraints on the shaped beams. 
     
     
       14. A communications system comprising:
 a receiver having a plurality of receiving elements and an output port; 
 at least one transmitter having a plurality of transmitting elements configured to transmit one or more signals to the receiving elements of the receiver via multiple wireless propagation channels; and 
 at least one active scattering platform located within the wireless propagation channels between the at least one transmitter and the receiver, the at least one active scattering platform being configured to receive and amplify the transmitted one or more signals and re-radiate the amplified received one or more signals toward the receiver, 
 wherein the receiver comprises a channel measurement unit configured to perform measurements of components of channel status information and generate a set of composited transfer functions by computing linear combinations of the measured components of channel status information, wherein the measured components of channel status information include a set of point-to-point transfer functions, each of the point-to-point transfer functions characterizing propagation paths between one of the transmitting elements and one of the receiving elements, wherein the composited transfer functions are multipoint-to-point transfer functions characterizing propagation paths between one or more of the transmitting elements and the output port of the receiver, and wherein each of the composited transfer functions is a linear combination of the point-to-point transfer functions, and 
 wherein the receiver uses the composited transfer functions to optimize amplitude and phase weighting of the re-radiated one or more signals. 
 
     
     
       15. The communications system of  claim 14 , wherein the channel measurement unit comprises a multiple-input-to-single-output processor for generating the composited transfer functions. 
     
     
       16. The communications system of  claim 14 , wherein the at least one active scattering platform is stationary or relocatable. 
     
     
       17. The communications system of  claim 14 , wherein the at least one active scattering platform has at least one of the group of variable amplification gain, shapeable receiving antenna gain, and shapeable transmitting antenna gain. 
     
     
       18. The communications system of  claim 14 , wherein the channel measurement unit comprises an optimization unit to perform optimization by continuously updating complex weighting for the re-radiated one or more signals received by the receiving elements of the receiver. 
     
     
       19. The communications system of  claim 18 , wherein the optimization unit uses optimization algorithms with performance constraints to obtain a set of optimized weights for a next update of complex weighting based on differences between current performances and the performance constraints. 
     
     
       20. The communications system of  claim 18 , wherein the optimization unit derives current performance using mathematical models and real-time measurements.